Add documentation on installation via Nix

[daspk04]

Hi @remicres and @vijdz !

I have added pyotb to Nixpkgs. It's available on both stable and unstable channel of nix packages, should work on any Linux distribution.

Installing a particular python version of pyotb from Nix packages will also install otb compiled for that python version c.f.
I also fix the environment variable OTB_ROOT to point to that otb, so an user don't have to set environment variable just importing pyotb should work. c.f

Installation via Nix:

nix-shell -p python312Packages.pyotb

# Example: specific channel:
nix-shell -I nixpkgs=channel:nixpkgs-unstable -p python312Packages.pyotb

# Example: specific channel and different python version:
nix-shell -I nixpkgs=channel:nixpkgs-unstable -p python313Packages.pyotb

Will it be possible to add this as an alternative option for installation to the documents ?

Thanks!

[vijdz]

@daspk04 ! All right, I will add it to the docs in the next release (probably next month)

[vijdz]

FYI regarding OTB_ROOT, there is a bug right now with OTB 9 (https://forgemia.inra.fr/orfeo-toolbox/pyotb/-/issues/124) but I found a fix that I already pushed in the branch release-2.2

[daspk04]

Hi @vijdz !

Thanks. I think at least for Nix it was less of an issue because it is already properly configured as we are building from source with Nix so the files generated from build are fixed based on build hash and likely to always exists.

The only part was we are not able to directly import it via python as it's not yet a python package and we have to reply on the OTB_APPLICATION_PATH and the file generated from the swig to be added to the PYTHONPATH . As the function set_environment seems to do that part when we set OTB_ROOT so that works.

Also documentation regarding Nix has been added to OTB may be you can also give it a try!